The interest in providing multimedia services such as TV in mobile communication systems is increasing. This is a service offered today by a plurality of operators throughout the world. The services offered today are based on a point-to-point communication, wherein each user of the service receives a specific content specified for that particular user/device. In a scenario wherein these services become popular, and a large number of users are interested in the same content at the same time, the point-to-point communication is not the most effective way of communication. Therefore, a number of broadcasting and multicasting techniques have been discussed with the aim of providing mobile TV, for example, in an efficient way in a mobile communication system. Such services are often referred to as Multimedia Broadcast and Multicast Service (MBMS) or Broadcast and Multicast Service (BCMCS).
The description of prior art and also the invention will have a starting point in the present mobile communication system referred to as UTRAN. UTRAN stands for UMTS Terrestrial Radio Access Network, and UMTS for Universal Mobile Communication System. The references to UTRAN and evolutions of UTRAN should be seen as non-limiting example. In the discussed evolutions of the present mobile communication systems, often referred to as E-UTRAN (Evolved UTRAN), the MBMS service will be offered in both mixed cells and dedicated MBMS cells. A mixed cell offers both unicast service such as speech, web browsing etc and MBMS service such as mobile television. In a mixed cell the MBMS service can be cell specific, that is, limited to a specific cell or it can be offered from multiple mixed cells. On the other hand in dedicated MBMS cell scenario, only MBMS service will be offered to a single or multiple dedicated MBMS cells in a coverage area. The availability of different services in different deployment scenarios is indicated to the user equipment, UE on MBMS specific control channels as done in 3GPP (Third Generation Partnership Program) Release 6.
In the following, various technological aspects and principles of MBMS transmission in UTRAN and E-UTRAN systems will be described.
MBMS Control Information
The 3GPP Release 6 supports following two control channels associated with MBMS transmission, see 3GPP TS 25.346, “Introduction of the Multimedia Broadcast/Multicast Service (MBMS) in the Radio Access Network (RAN); Stage 2”.3GPP TS 25.331, “Radio Resource Control Protocol Specifications”:                MBMS control channel (MCCH)        MBMS notification indication (MICH)        
MCCH is a logical channel, which carries control information related to MBMS service, MBMS radio bearer etc. MCCH is also present in E-UTRAN, where it shall be mapped onto an appropriate transport channel depending upon the deployment scenario such as single cell or multiple cell MBMS transmission. The transport channel carrying MCCH is in turn mapped onto one or more resource blocks (physical channel resource). The MBMS service itself is sent on MBMS logical traffic channel called MBMS traffic channel (MTCH).
The MBMS notification is in principle similar to MICH in release 6, which is used to inform the UE about changes in MCCH information. Thus MICH in release 6 allows the UE to read MCCH in case there is change in the service information. This will prevent the UE from continuously reading MCCH thereby saving the UE power consumption. Currently the working assumption is that in E-UTRAN there is no separate channel to send MBMS indication. Instead, the MBMS notification is sent on the normal downlink control channel, which also contains other type of control informations. It is generally termed as L1/L2 (Layer 1/Layer 2) control channel since it carries information related to the lower layers.
The MCCH resource allocation (e.g. resource block, time instances etc) will be indicated in system information (BCH). This means that after acquiring synchronization, the UE shall first read the system information (BCH) and obtain MCCH. The MCCH will contain information pertaining to the offered MBMS services as well as the resource allocation for the MBMS notification.
MBMS Scenarios
As discussed above MBMS multi-cell transmission will be offered both in mixed cells and in MBMS dedicated cells. The two scenarios are described below:
In a mixed cell, where both unicast and MBMS services are offered, two main scenarios with respect to MBMS transmission are considered:                Single cell MBMS transmission        Multi-cell MBMS transmission        
For all single cell or cell specific MBMS transmissions MCCH can be sent on the downlink shared channel (DL-SCH). The MBMS notification will be sent on L1/L2 control channel. The corresponding MBMS service (i.e. MTCH) will also be mapped onto DL-SCH. On the other hand MBMS multi-cell scenario should support single frequency network (SFN), enabling SFN combining (i.e. combining in the air). This means the same service should be sent on the same physical resource in all the multi-cells, which are SFN combined. Similarly the MBMS control channel should also be SFN combined, i.e. it must also share the same physical resources in all combined cells. Secondly all the resource blocks containing MBMS shall use the common scrambling code in all the mixed cells within the SFN area. It should be noted that the unicast and multi-cell MBMS services (i.e. which are SFN combined) can be multiplexed in time domain, in frequency domain or in combination thereof. The MBMS transmission via SFN is generally abbreviated as MBSFN.
In dedicated MBMS cell scenario only MBMS service is transmitted. This is typically only a multi-cell transmission scenario. The MBMS services are sent over the entire single frequency network (SFN) area using the same resource blocks in all the cells to facilitate SFN combining. Similarly the MBMS control channel should also be SFN combined.
In principle the multi-cell MBMS transmission in both mixed and MBMS dedicated cells is quite similar. This paves the way for similar solution for MBMS control information transmission and activation in the two scenarios.
MBMS Resource Allocation
Due to SFN combining for multi-cell MBMS transmission, the radio resources (resource blocks, sub-frames etc) are allocated in a centralized manner by a central MBMS server or MBMS gateway, which will be connected to all the base stations (or Node B) belonging to the SFN network.
UE Locations in Variable Bandwidth Scenario
In current systems such as UTRAN the UE reception bandwidth is the same as the cell transmission bandwidth. However in E-UTRAN, and other evolutions of the current systems, the system may employ variable bandwidth, which means for example 10 MHz in some cells and 20 MHz in another set of cells even within the same coverage area. Furthermore, the UE minimum bandwidth can be smaller than the network bandwidth. One example is that a 20 MHz UE is operating in a system with a 40 MHz cell transmission bandwidth. The MBMS control channel transmission should be such that a UE with smaller bandwidth than the cell bandwidth (e.g. 20 MHz UE operating in 40 MHz cell bandwidth) should be able to receive the MBMS control information within its reception bandwidth.
In order to limit the system and UE complexity a 20 MHz UE operating within 40 MHz cell bandwidth, shall be placed at two or three limited positions. Because this will require UE to tune its receiver only to few specific positions in frequency domain within a cell. FIG. 1 shows an example of a 20 MHz UE with two different positions in the frequency domain: lower (left) 20 MHz or upper 20 MHz (right).